It is well known that, especially in the cosmetic industry, an important technical problem or requirement refers to the stability of water-containing formulations, such as cosmetic, dermatologic, pharmaceutical or veterinary formulations. In order to avoid the phases or components of corresponding formulations and emulsions to separate, water-containing formulations, like solutions, emulsions or suspensions are often thickened to higher viscosities by adding thickening agents or compositions. Ideally, these thickening agents should provide the desired thickening properties or viscosity stability over a wide pH range and also in the presence of electrolytes.
One approach for improving the stability of standard thickeners in the cosmetic field is based on the use of crosslinked polymers containing strongly acidic monomers. Crosslinked polymeric thickener compositions are, for example, suggested in EP 0 503 853. More precisely, a thickening composition containing a water-soluble polymeric material comprising units derived specifically from acrylamide and 2-acrylamido-2-methyl-propanesulfonic acid (with at least partially neutralized units) and N,N′-methylene-bis-acrylamide (used in a specific amount of from 0.06 to 1 millimole per mole of total monomer units) is described in EP 0 503 853.